Some people are just naturally better at comparing—matching—different visual patterns (faces, firearms, fingerprints) side by side

Match me if you can: Evidence for a domain-general visual comparison ability. Bethany Growns, James D. Dunn, Erwin J. A. T. Mattijssen, Adele Quigley-McBride & Alice Towler. Psychonomic Bulletin & Review, Jan 7 2022. https://link.springer.com/article/10.3758/s13423-021-02044-2

Abstract: Visual comparison—comparing visual stimuli (e.g., fingerprints) side by side and determining whether they originate from the same or different source (i.e., “match”)—is a complex discrimination task involving many cognitive and perceptual processes. Despite the real-world consequences of this task, which is often conducted by forensic scientists, little is understood about the psychological processes underpinning this ability. There are substantial individual differences in visual comparison accuracy amongst both professionals and novices. The source of this variation is unknown, but may reflect a domain-general and naturally varying perceptual ability. Here, we investigate this by comparing individual differences (N = 248 across two studies) in four visual comparison domains: faces, fingerprints, firearms, and artificial prints. Accuracy on all comparison tasks was significantly correlated and accounted for a substantial portion of variance (e.g., 42% in Exp. 1) in performance across all tasks. Importantly, this relationship cannot be attributed to participants’ intrinsic motivation or skill in other visual-perceptual tasks (visual search and visual statistical learning). This paper provides novel evidence of a reliable, domain-general visual comparison ability.

General discussion

Across two experiments, we explored whether there is a generalizable and domain-general perceptual skill underpinning the ability to compare—or “match”—different visual stimuli. Participants’ sensitivity in four different comparison tasks were all significantly correlated with each other, and a substantial portion of variance (41.99% in Experiment 1 and 34.92% in Experiment 2) across all tasks was accounted for by one shared “matching” component in both experiments. Together, these results support the conclusion that individual differences in visual comparison accuracy are explained by a shared ability that generalizes across a range of visual stimuli. Notably, intrinsic motivation (Experiment 1), visual search and visual statistical learning (Experiment 2) did not significantly correlate with sensitivity in any comparison task and loaded onto separate components that accounted for large proportions of the variance across all tasks (20.95% in Experiment 1 and 19.07% in Experiment 2). This suggests that individual differences in visual comparison cannot be attributed to individual differences in intrinsic motivation or other visual-perceptual tasks.

Importantly, our study also provides evidence of stimulus-specific individual differences. This is reflected in the moderate correlations seen between sensitivity in all comparison tasks across both experiments, and the principal components analysis, where additional components featured loadings from just one or a subset of comparison tasks. This suggests there are also likely individual stimulus-specific skills where some people are better at comparing specific stimuli over other stimuli. Overall, our results are the first to suggest that visual comparison is an interplay between an overarching generalizable comparison ability, as well as individual stimulus-specific ability.

This stimulus-specific skill may be partially attributed to stimulus familiarity and experience. Face-comparison performance—the most familiar stimuli—demonstrated the highest stimulus-specific variance: face-comparison sensitivity had the lowest average correlation with all other tasks (r = .267 in Experiment 1 and .289 in Experiment 2); and accounted for the third to fourth-largest portion of variation (16.37% in Experiment 1 and 11.55% in Experiment 2) across all tasks. In contrast to faces, fingerprint, firearms and artificial-print sensitivity accounted for less variance in our data—where familiarity with these stimuli ranges from unfamiliar to entirely novel. This is consistent with research that suggests there is a shift from domain-general to domain-specific mechanisms with increased perceptual experience in a domain (Chang & Gauthier, 2020, 2021; Sunday et al., 2018; Wong et al., 2014; Wong & Gauthier, 2010, 2012), and research that links experience and visual comparison performance (Thompson & Tangen, 2014).

Our results highlight visual comparison as a natural and generalizable ability that varies in the general population—yet the precise mechanisms underpinning this skill are only beginning to be explored (see Growns & Martire, 2020b, for review). It is possible that holistic processing—or the ability to view images as a ‘whole’ rather than a collection of features (Maurer et al., 2002)—underpins visual comparison performance: both facial and fingerprint examiners show evidence of holistic processing when viewing domain-specific stimuli (Busey & Vanderkolk, 2005; Towler, White, & Kemp, 2017b; Vogelsang et al., 2017). In contrast, featural processing—or the ability to view images as separate features—is also important in visual comparison. Professional performance is improved when examiners have an opportunity to engage featural processing: both facial and fingerprint examiners demonstrate greater performance gains than novices in domain-specific visual comparison tasks (Thompson et al., 2014; Towler, White, & Kemp, 2017; White, Phillips, et al., 2015). Novices’ face-comparison performance also correlates with featural processing tasks such as the NAVON and figure-matching tasks (Burton et al., 2010; McCaffery et al., 2018), and novices’ comparison performance is improved by instructing participants to rate or label features (Searston & Tangen, 2017c; Towler, White, & Kemp, 2017b). Low-performing novices also derive greater benefit from featural comparison training than high-performers—suggesting high-performers may already use such strategies (Towler, Keshwa, et al., 2021b). The role of holistic and featural processing in visual comparison performance remains an important avenue for future research.

These results have important applied implications. Whilst empirically based training for existing examiners is important to improve ongoing professional performance (Growns & Martire, 2020a), our results suggest that larger gains in performance could be achieved by selecting trainee examiners based on visual comparison ability. A similar approach has been used in applied domains: recruiting individuals with superior face recognition improves performance in real-world face identification tasks (Robertson et al., 2016; White, Dunn, et al., 2015). Professional performance in other forensic feature-comparison disciplines could likely be similarly improved by recruiting individuals with superior performance on a test battery of visual comparison tasks. Importantly, our results do not suggest that examiners would benefit from practicing outside of their primary domain of experience. Despite identifying a generalizable visual comparison ability, we also identified individual differences in stimulus-specific skills that suggest part of accurate visual comparison performance is domain specific.

As the participants in this study were untrained novices, it is unclear whether these results could generalize to practicing professionals. While investigating individual differences in the general population requires a novice sample, it is entirely plausible that a domain-general visual comparison mechanism may be diminished or negated for experts in this task as expertise is typically conceptualized as narrow and domain-specific (Charness et al., 2005; Ericsson, 2007, 2014). However, emerging evidence suggests domain-specific expertise may lend advantages to domain-general skill. For example, although facial examiners outperform fingerprint examiners in face comparison (i.e., facial examiners’ domain-specific expertise), fingerprint examiners outperform novices in the same task—despite it being outside their primary area of expertise (Phillips et al., 2018). Whether this domain-general advantage is developed alongside domain-specific expertise or is the result of preexisting individual differences in this ability will be an important avenue for future research.

This study provided the first evidence of a generalizable ability to underpinning the ability to compare or “match” different, complex visual stimuli. We demonstrated that the ability to compare stimuli such as faces, fingerprints, firearms, and artificial prints is in part due to a generalizable and domain-general ability—although subject to stimulus-specific constraints. These results have important theoretical and applied implications for both behavioural and forensic science. Importantly, test batteries of visual comparison tasks could be used to identify and recruit top-performing individuals to improve performance in forensic feature-comparison disciplines.